The present invention relates, in general terms, to wheel hubs and is aimed, more particularly, at those intended for equipping industrial vehicles or agricultural or public works equipment.
Being more specifically a driving wheel hub, such a wheel hub conventionally takes the form of a hollow body in which a reduction gear is located, to bring the rotational speed to a permissible value, the sun gear shaft of the reduction gear being designed to be rotationally fast with the corresponding wheel shaft, while the planetary gear carrier of the reduction gear is fixed to the hollow body.
A brake must be associated with such a hub, and this brake must be subjected to at least one control, or operating control.
This can be, especially, a disc brake.
In such a case, this brake usually comprises only a single brake disc, and this brake disc is located outside the hollow body of the wheel hub in question, between the latter and the axle at the end of which the wheel hub is mounted.
Being thus open to the surroundings, this brake is subjected to all kinds of material thrown up, to the detriment of its operation and its useful life.
Moreover, it is not readily accessible, and, in practice, to change its brake pads after wear, it is necessary first of all to remove the wheel mounted on the wheel hub in question, and this is relatively difficult when, as in this particular case, a wheel of large diameter is concerned.
However, to avoid these disadvantages, it has already been proposed to locate the brake at the end of the wheel hub with which it is associated, that is to say beyond this wheel hub in relation to the axle at the end of which the latter is itself mounted.
In such a case, the brake can, for example, be mounted in a special compartment which protects it from the surroundings, while making it possible to use, as before, friction linings which work in a dry state.
Alternatively, it can be mouned in a compartment communicating with the hollow body of the wheel hub with which it is associated and can consequently run in the oil present in this hollow body for the purpose of lubricating the corresponding reduction gear.
The advantage which can be achieved, in this case, from such an arrangement is nomally twofold: on the one hand, the oil in question, which is kept in circulation, participates in dissipating the heat energy generated during braking, and, on the other hand, it minimises the wear of the friction linings and, in practice, avoids the need for any maintenance.
However, this being so, since the coefficient of friction is lower, the brake to be used must be a multidisc brake, that is to say a brake comprising a plurality of brake discs alternating with interpolated discs.
The brake discs are rotationally fast on the corresponding shaft, while the interpolated discs are rotationally fast on the hollow body.
Since such discs must also be movable axially to allow axial clamping of the brake discs during braking, a splined assembly is conventionally provided both between the brake discs and the corresponding shaft and between the interpolated discs and the hollow body of the hub.
Although such an assembly of a multidisc brake at the end of a wheel hub may thus be satisfactory, in practice it leads to difficulties.
First of all, although the splined assembly between the brake discs and the corresponding shaft does not of itself present too much difficulty because it acts on a relatively small and inside diameter, the same is not true of the splined assembly between the interpolated discs and the hollow body of the hub.
In fact, such a splined assembly acts on a relatively large and outside diameter.
Now, for the necessary axial mobility it is indispensable that play be provided between the interpolated discs and hollow body in the corresponding splined assembly, and, because this splined assembly acts on a relatively large and outside diameter, this play must itself be necessarily relatively large to allow for the thermal expansion taking place during operation, this then being unfavorable since it leads to a reduction in play, whereas on an inside diameter it leads to an increase in this play and is, on the contrary, favorable.
Because of the reciprocating movement which the interpolated discs undergo during operation, this play is the cause of damage to the splines of this splined assembly, and this can result in their destruction.
Furthermore, since it is possible, in practice, to fill the hollow body of the wheel hub in question only partially with oil, to prevent an excessive loss of power as a result of braking during operation and to prevent the development of a leak to which the oil would inevitably be subject during operation because of its thermal expansion if the initial filling was total, there arises, during operation, an oil ring in the hollow body as a result of centrifuging, the oil abandoning the central part of this hollow body to collect in the peripheral part of the latter, in such a way that the friction linings of the brake discs can then no longer run in the oil and they function in a dry state, to the detriment of their useful life, since these friction linings are not normally intended for such dry operation.
Moreover, although the circulation of oil is sufficient to dissipate the energy during braking below relatively moderate speeds, for example of the order of 40 km/h, it seems, in practice, too limited beyond this, and especially so when the brake is used for slowing down.
Finally, this oil, which is a so-called extreme-pressure oil, the qualities of which have been selected to correspond to those necessary for the reduction gear, is not suitable for the brake: it is desirable, for the reduction gear, that the oil should have a high shearing resistance, whereas it is desirable, for the brake, that it should have, on the contrary, a low shearing resistance.
An object of the present invention is in general terms, to provide arrangements which make it possible to avoid these disadvantages.